The present embodiments relate to shielding for an electronic circuit.
Magnetic resonance tomography (MRT or MR; also referred to as MRI for Magnetic Resonance Imaging) is an imaging method that may be used in medical diagnostics for presenting structure and function of the tissue and organs. MRT is based physically on the principles of nuclear magnetic resonance and is therefore also referred to as nuclear magnetic resonance tomography.
Slice images of a human or animal body may be created with MRT. The slice images allow the organs and many pathological changes to organs to be assessed. Magnetic resonance tomography is based on strong magnetic fields and also electromagnetic alternating fields in the radio frequency range. Specific atomic nuclei (e.g., the hydrogen nuclei/protons) are resonantly excited in the body with the strong magnetic fields and the electromagnetic alternating fields. The resonantly excited atomic nuclei induce electrical signals in the receiver circuit. No stressful x-rays or other ionizing radiation is generated or used in the device. A basis for the image contrast is different relaxation times of different types of tissue. The different content of hydrogen atoms in the different tissues (e.g., muscle, bones) also contributes to the image contrast.
In addition to the static basic magnetic field, switched gradient magnetic fields in the Kilohertz range and the MR frequency in the upper Megahertz range (e.g., 60-500 MHz and often 123 MHz) are used for MRT. As integration progresses, there is an increasing requirement for the electronics modules such as A/D converters or field programmable gate arrays (FPGAs), for example, to be disposed directly on the highly-sensitive receive coils. In such cases, the electronics modules may interfere with the reception of the MR signals in that the electronics modules emit frequencies or frequency portions in the range of the MR frequency. These electronic components are thus to be shielded accordingly.
The shielding for the electronic modules is to be as high as possible in the range of the MR frequency and is to be as transparent as possible however for the gradient frequency (e.g., the shielding is to possess a lowpass characteristic).
It is known that electronic modules may be shielded with the aid of full-coverage metal boxes or metal covers. The disadvantage, however, is that, on account of the full-coverage metal surfaces, eddy currents may be induced on such shielding. The eddy currents lead to image faults during magnetic resonance tomography. Therefore, the electronics modules causing the interference are disposed at a safe distance and connected to the receive antennas by cables. This increases the complexity of the cabling, which overall has an adverse effect on safety as well as causing the costs of such a solution to rise.
Publication WO 2008/051915 A1 shows shielding of an electronic circuit, in which metal structures are embodied on both sides of a substrate. Each of the metal structures includes non-contiguous part areas with slots lying between.
A cylindrical shield for magnetic resonance antenna is described in publication U.S. Pat. No. 5,367,261 A, in which metal structures with predefined patterns are provided on both sides of a substrate.